SEAMO 2027 - Paper D - SET 05 - Self-study Question 2

Trapezium $ABCD$ has parallel bases $AB=30$ cm and $CD=40$ cm, with $AD=BC$. Diagonals $AC$ and $BD$ intersect at $M$. If its area is $490$ cm$^2$, find the area of triangle $BCM$ in cm$^2$.